1. Field of the Invention
This invention is a heat-shrinkable, heat-sealable, biaxially oriented polyester film and method of making such film.
In particular, such invention is a novel essentially polyethylene terephthalate film usable in making shrink packages having improved seals and improved optics.
These improved features are primarily the result of the film having:
A relative viscosity of at least 1.80; PA1 Substantially balanced latent shrinkage; PA1 A low shrinkage force; PA1 A melting point of from about 215.degree. C. to 230.degree. C.; and PA1 Haze of less than 5%. PA1 wrapping the film about an article to be packaged; PA1 bringing surface portions of the film into abutting contact with each other; PA1 heat sealing such abutting portions together; and PA1 shrinking the film into skin-like contact with the article (or parts of it) to form the skin package. PA1 a relative viscosity (at 1% concentration in 60/40 tetrachloroethane/phenol at 30.degree. C.) of at least 1.80; PA1 substantially balanced latent shrinkage within the range from about 31% to 47% at 100.degree. C.; PA1 an average shrinkage force of less than about 1,000 psi at 100.degree. C.; PA1 a melting point of from about 215.degree. C. to 230.degree. C.; and PA1 haze of less than 5%.
2. Description of the Prior Art
U.S. Pat. No. 2,928,132 to Richards is exemplary of the prior art. Such patent discloses a method of producing a shrinkable polyethylene terephthalate film having substantially the same degree of shrinkage in both directions of the film.
Canadian patent 694,367, another example of the prior art, shows a process for the manufacture of shrinkable seamless tubular foils of polyethylene terephthalate, which films shrink on heating to above 90.degree. C. by more than 30% in each superficial direction.
While these patents show the making of heat-shrinkable polyester films they do not show the making of the improved film of this invention with its critical properties, as made by the novel method also of this invention, whereby such film is capable of being used in making shrink packages having improved seals and improved optics.